1. Field of the Invention
This invention relates to method and apparatus for rotationally orienting a fluid conducting conduit. More specifically, the invention relates to orienting and steering a subterranean drilling assembly such as used in drilling an oil or gas well.
2. Setting of the Invention
In order to enhance the recovery of subterranean fluids, such as oil and gas, it is sometimes desirable to orient the direction of the wellbore or borehole. For example, in an oil producing formation or strata which has little vertical depth and relatively greater horizontal extent with respect to the surface of the earth, a wellbore which extends horizontally through the oil producing zone may be more productive than one extending vertically.
In order to drill a wellbore horizontally, or at any selected angle, it is necessary to be able to steer the drilling bit at the end of the fluid conducting conduit, known as the drill string. U.S. Pat. No. 4,699,224, issued to Burton, discloses such apparatus and method, and is incorporated herein by reference thereto.
U.S. Pat. No. 4,699,224 discloses a method of horizontal drilling using a flexible drill string connected by a flexible joint to a drill bit collar. The drill bit collar is equipped with a stabilizer and a rotary drill bit. An eccentric cylindrical collar is used which circumferentially mounts to the downhole end of the flexible drill string over the flexible joint connected to the drill bit collar. The flexible joint rotates with the drill string within the eccentric collar. The thicker wall at one side of the eccentric collar forces the flexible joint to the opposite side of the wellbore which causes the drill bit to pivot about the flexible joint in the opposite direction of the deflection created by the eccentric collar. A borehole engaging means is mounted on the outside surface of the thicker wall of the eccentric collar.
The borehole engaging means, commonly called a "razorback" is used to rotationally orient the eccentric collar, i.e., the razorback engages the side of the borehole when the drill string is rotated in one direction and locks the eccentric collar to the wellbore thus rotationally orienting the eccentric collar with respect to the borehole. When the drill string is rotated in the opposite direction, the razorback disengages from the wellbore and a spring-biased latch mechanism latches the eccentric collar to the drill string and causes the eccentric collar to rotate with the drill string. This allows the eccentric collar to be rotationally reoriented with respect to the wellbore.
Although the borehole engaging means, or razorback, is designed to prevent the cylindrical eccentric collar from rotating with the drill string during drilling, friction between the eccentric collar and drill string together with downhole vibration and movement occurring during drilling will tend to rotate the collar, thereby resulting in the need to reorient the eccentric collar periodically. Normally, the razorbacks are oriented to the high side of the wellbore, i.e., the side of the wellbore closest to the surface of the earth, in order to drill a vertically planar curve.
At least two problems arise in the downhole operation of the razorbacks. The first problem is orienting the razorback to the high side of the wellbore (or any other selected side of the wellbore) while in the nondrilling mode, i.e., while rotating the drill string in the reverse direction. The second problem is maintaining orientation of the razorback and eccentric collar while drilling.
The first problem occurs during the reorientation of the razorback. The reorientation procedure consists of periodically raising the drilling assembly off the bottom of the wellbore and rotating the drill string backwards, normally counterclockwise, less than or nearly one full turn to a selected rotational orientation. At some point during this reverse rotation, a pawl or latch is supposed to engage the eccentric collar and cause the eccentric collar to be rotated with the drill string. Latch engagement has not been readily achieved in drilling tests because the latch spring breaks, the latch plugs with rock debris and drilling mud solids, etc.
The second problem of maintaining the razorback orientation during drilling arises because there has been no reliable method of sensing the rotational orientation of the razorback within the wellbore. U.S. Patent Application Ser. No. 07/281,293 attempts to provide a high side signal, i.e., a signal when the razorback is at the high side of the wellbore, by restricting flow through the drill string with a ball which is gravitationally rotated in a toroidal race. Flow through the drill string is divided between a primary flow port and a signal port. The ball is supposed to block the signal port when the signal port is on the lowest side of the wellbore and thereby increase the fluid pressure in the drill string upstream of the signal port. This increase in fluid pressure is a signal that the conduit, or drill string, and anything connected thereto is in a known rotational orientation. A problem with the apparatus and method of U.S. Patent Application Ser. No. 07/281,293, is that the ball gets stuck over the signal port due to hydraulic effects, i.e., the fluid flow through the drill string and signal port pulls the ball into the signal port.
Therefore, there is a need for an apparatus and method which will rotationally orient a fluid conducting conduit, such as a drill string, and also orient a collar, such as the eccentric collar, on the fluid conducting conduit. It is contemplated that such an apparatus and method will allow more accurate steering of subterranean drilling assemblies and result in higher production rates of oil and gas. It is also contemplated that such an apparatus and method will allow more accurate orientation of rotatable fluid conducting conduit and collars in virtually any environment.